After getting tired of Walmart style "smart battery chargers", which were not very smart and did not charge things well, I changed my mind and decided to follow advice of rec.crafts.metalworking members who suggested to use a big old iron type power supply.
I bought this PP-1104B/G, in a lot with PP-1104C/G. PP-1104B/G is very similar to PP-1104C/G, with differences being purely cosmetic.
I tried using one to charge my deep cycle batteries. I noticed right away that it has a very annoying quirk. When powered off, if connected to a battery, it exhibited "reverse current", with the battery quickly drained through the power supply. I think that it is due to the supply having a big capacitor bank and a beefy discharge resistor -- so that the battery would discharge itself through that resistor.
That problem was solved by adding a diode to the output so that DC current can only flow one way. Problem was solved. (see pictures)
I also added clamps, and casters to this power supply so that it can be easily moved.
I will also buy and install a Intermatic timer to it so that I can limit the amount of time that the charger runs before shutoff. I will buy one that has a hold capability in addition to timer capability.